At least some example embodiments of the inventive concepts described herein relate to a semiconductor memory device, and more particularly, relate to a nonvolatile memory device and its operating method.
Semiconductor memory devices may be volatile or nonvolatile. The volatile semiconductor memory devices may perform read and write operations at a high speed, but contents stored therein may be lost at power-off. The nonvolatile semiconductor memory devices may retain contents stored therein even at power-off. The nonvolatile semiconductor memory devices may be used to store contents which must be retained regardless of whether they are powered.
The nonvolatile semiconductor memory devices may include a mask read-only memory (MROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), and the like.
A flash memory device may be a typical nonvolatile semiconductor memory device. The flash memory device may be widely used as a voice and image data storing medium of information appliances such as a computer, a cellular phone, a PDA, a digital camera, a camcorder, a voice recorder, an MP3 player, a handheld PC, a game machine, a facsimile, a scanner, a printer, and the like.
As a demand on high integration of a memory device increases, there is being used a multi-bit memory device, which stores multiple bits in a memory cell.